In the state of the art beverage preparation machines are known, which include an injection assembly for injecting a hot fluid into a capsule containing beverage ingredients, in order to brew and dispense a beverage. Typically such beverage preparation machines further include a reservoir for storing a fluid, a heater for heating the fluid received from the reservoir, an air separator for removing air from the heated liquid, and an injection assembly for piercing the capsule and for injecting the fluid into the capsule. In most cases a check valve is located between the air separator and the piercing needle. The check valve opens when fluid is pressurized upstream, and otherwise closes to prevent backflow into the machine.
WO 2009/135899 A1 discloses a beverage preparation device according to the above-described state of the art. The beverage production device comprises means to hold a capsule, means for heating and supplying a fluid, and means for injecting the hot fluid into the capsule. The machine particularly discloses a check valve, which is connected between an air separator and a fluid line to an injection member.
FIG. 1 of the present application shows the check valve, which is used in WO 2009/135899 A1. The check valve has a water inlet 1a and a water outlet 2a. The check valve design has the disadvantage that between the preparations of two beverages, a large dead volume 3a of hot fluid remains between the check valve and the piercing needle. FIG. 1 shows that the dead volume 3a appears particularly in cavities within the check valve and in a fluid line downstream of the check valve.
Any dead volume of fluid in a beverage preparation machine is disadvantageous due to safety and health issues. A dead volume can promote the development of bacteria, for example bacteria originating in and/or migrating into the dead volume from a used capsule, which has not yet been ejected or removed from the beverage preparation machine.
EP 2 395 269 A1 discloses a check valve having a reduced dead volume. The check valve 1 is shown in FIG. 2a of the present application and comprises a main body 2b and a plug member 3b inside the body 2b. The plug member 3b is subjected to an elastic load 4b housed inside a cavity of the body 2b. The plug member 3b is movable. The check valve further comprises a conduit 9b, along which a pressurized fluid may flow. In an open position of the plug member 3b, the fluid can flow past a head part of the plug member 3b, whereas in a closed position of the plug member 3b the fluid flow is interrupted by the head part of the plug member, since the head part engages with a seat 19b. The conduit 9b further has an off-take conduit 32b connecting to a chamber 30b. Due to the off-take conduit 32b the fluid in the conduit 9b can exert a pressure on a first surface 26b of the plug member 3b, and can move the plug member 3b to its open position, if the fluid pressure exceeds a predetermined threshold.
FIG. 2b shows how such a check valve can be integrated with an air separator in a beverage preparation machine. The check valve, however, has the disadvantage that it leaves still a too important dead volume downstream of the check valve, and moreover takes a lot of space in the machine due to its bulky configuration.
In view of the above, the object of the present invention is to overcome the disadvantages of the prior art. In particular, the object of the present invention is to provide a check valve, an injection assembly and a beverage preparation machine, which reduce the risk of bacteria development due to a reduced dead volume, and can additionally be built more compact.